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Crystal Lattices as Refrigerators: Scientists Pump Heat With Crystals

A recent simulation conducted at the Carnegie Institution suggests that it’s possible to use crystals to pump heat efficiently, making them useful as a method of refrigeration. We may soon see crystals, instead of metal heat sinks, on our computer chips.

The study, led by Maimon Rose and Ronald Cohen, simulated the behavior of a special class of crystals, called ferroelectric crystals. These crystals maintain a constant electrical polarization even when an electric field is not present. In this sense, they are similar to ferromagnets, like your refrigerator magnet, which maintain a magnetic field of their own even if no external field is applied.

This unique feature makes ferroelectric crystals and materials useful for all kinds of things, such as memory storage, sensors, and capacitance. They are used in ultrasounds, acting both as generators and sensors, as well as high-def infrared cameras (their sensitivity allows them to measure temperature changes less than a millionth of a degree Celsius).

By applying an external electric field, it is possible to change the direction of the crystal’s internal field, which stays intact after the external field is shut off. The simulation revealed that it should be possible to dramatically raise the temperature of the crystal lattice with such a field.

The material simulated was lithium niobate. While scientists have been aware of this heat pump effect since the 1930s, they were not aware it was possible to achieve temperature changes this dramatic.

This was the first time such a study was conducted on lithium niobate. Previous studies involved materials with a high transition temperature, which keep their ferroelectric properties in warmer temperatures. This study demonstrated that a crystal with a lower transition temperature was actually more effective, because it could pull in a great deal more heat.

It will be interesting to see how this plays out in physical applications.